I have and idea.

General CNC CNC Routers
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I have and idea. I’m submitting it here to you capable folks because I do not feel that I have the resources to take advantage of it.

It’s an idea to build a simpler rotary 4th axis for cnc, with a fraction of the parts.

It works kind of like an automatic tool changer, you would move the carriage to a certain place then the z axis would actually operate the A (rotary) axis position. There would need to be some kind of linkage between the carriage and the A axis.

I’m not sure precisely what that would look like. Maybe a star disk (5 or 6 lobe). The Z would go down to the bottom then have to come back again (several times) if you wanted to do 360deg.

You would need a few more pieces though.

The A axis would need to stay in precisely the position it is placed, for that it needs some sort of brake. I would immediately think a disk brake from a bike would be a good way to go, but there are many ways to skin that cat. There would need to be an actuation for this brake, such as a solenoid or you could use a stepper or servo (giving up the lower complexity). An encoder wouldn’t be a bad idea either.

Then there would be the software.
I will post this over to Smoothieware and CNCWeb communities as well to see if anyone wants to give it a whirl.

http://cdn4.explainthatstuff.com/typical-cam-shapes.png

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I’m curious how you see the tool movement being controlled if your Z movement is being used elsewhere. I’ve read about setups that allow you to swap your x or y axis onto your a axis, so you still only have three axes, but one is rotary. That makes some sense to me. I’m struggling to figure out how to cut material when I don’t have independent control over the tool height.

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Much like a tool changer once the A axis is in place the carriage can move back over to the work piece…

It’s not a solid linkage.

It could be a simple vertical rod with a bearing at the bottom.

If the A axis rotates around the x axis then the bearing would be oriented along that axis too. …

When you move the assembly (carriage+rod+bearing) to a set position, the bearing interfaces with the cam and you can turn the A axis.

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Same as this… just rotate it 90deg and add the brake and cam.

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@John_Bump as I comprehend what is being said, like a tool changer things only happen when the head is in a specific position. It seems like what is being suggested is the loss of a bit of Y axis volume to make the A axis function. Instead of 500mm you might give up 5mm or less and to actuate the A axis you would move the head to Y -5 or something similar. That way when the head is to the negative of machine home you are moving the A axis.

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Edit: In the comment above when I said X axis I did in fact mean Y Sorry for the confusion…
Thanks to @Kyle_Kerr for helping me see my little error…

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@Kyle_Kerr I believe you have the right idea…

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The real problem I would see with your idea is all out the extra movement required to adjust the rotary axis. Your CAM software would have to be aware of the way the A axis is actuated because things wouldn’t work as nicely/easily as they do with a powered rotary axis.
I don’t mean to rain on your parade, but, your idea seems like a solution in search of a problem. At least as I comprehend what you are suggesting.

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Seems like alot of times you would only need a few moves to get all the way around an object.

4th axis is often really used as 3.5axis…

As in the machine can get everything in a 180 degree manifold, making only 2 moves.

Or maybe you have a shorter bit and need more detail. So you have to move every 60degrees to get around your object.

It wouldn’t truly replace a real 4th axis, but it could save you having to go in and reposition your piece for different operations.

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Just when I think I’m making head or tail from cnc machines someone post something that makes no sense to me. I feel like a tree at the end of a runway.

Is what’s being said that when the y axiz moves to for example -5 the steppers engage via a cam to turn the work instead of the gantry thus moving the work like a lathe or turn table would.

And my question what is the saving in tooling to do this seems like at most you’re saving one stepper motor and driver.

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The 3.5 axis idea makes a ton of sense. I could use that. A lot of my work is sequential setup for dofferent faces.

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@Michael_Scholtz ​ check out the xatc video I posted above…
He uses the cnc movement to turn the tool turntable.

This is essentially the same idea but using that motion for a 4th axis.

Yes, mainly saving 1 stepper and driver. Maybe it’s a better idea for prebuilt cncs that want another axis rather than diy cncs that can add any axis they want :confused: